RPC client pipefs dentries cleanup logic has been changed:1) Cleanup is done now in separated rpc_remove_pipedir() function, which takescare about pipefs superblock locking.

Also this patch removes slashes from cb_program.pipe_dir_name and fromNFS_PIPE_DIRNAME to make rpc_d_lookup_sb() work. This doesn't affectvfs_path_lookup() results in nfs4blocklayout_init() since this slash is cuttedoff anyway in link_path_walk().